This application claims the benefit of Korean Patent Application No. 1999-38155, filed on Sep. 8, 1999, under 35 U.S.C. xc2xa7 119, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a backlight device, and more particularly, to a backlight device for use in a liquid crystal display (LCD) device.
2. Description of Related Art
FIG. 1 shows a conventional backlight device for use in an LCD device. As shown in FIG. 1, the conventional backlight device 100 includes a light source 10, a U-shaped lamp holder 15 having a lamp reflector 16, a light waveguide plate 40, a reflector 50, and a prism sheet 20. The light source 10 is located adjacent to an end 40a of the light waveguide plate 40, and most of the light source 10 is surrounded by the lamp holder 15. The end 40a constitutes a surface through which the incident light from the light source 10 is emitted. The prism sheet 20 is arranged on a front surface 40b of the light wave guide plate 40, and the reflector 50 is located under a bottom surface 40c of the light wave guide plate 40.
The emitted light from the light source 10 is directed toward the surface 40a of the light waveguide plate 40 by the lamp reflector 16 and is then directed either toward a prism sheet 20 or a reflector 50. The light reflected by the reflector 50 is emitted toward the observer through a prism sheet 20, and a liquid crystal panel (not shown) in the form of an information.
FIG. 2 is a graph illustrating brightness with respect to an angle of light passing through the prism sheet. As shown in FIG. 2, brightness distribution is discursive. In other words, light passing through the prism sheet 20 is not well collimated. As a result, light collimating efficiency is bad, and collimating loss takes place at portions xe2x80x9cAxe2x80x9d. In addition, in the conventional backlight device of such a structure, it is not easy to narrow an angle of light passing through the prism sheet to a desirable angle range (for example, from xe2x88x9240 degrees to +40 degrees).
For the foregoing reasons, there is a need for a backlight device having a high light collimating efficiency.
To overcome the problem described above, preferred embodiments of the present invention provide a backlight device having a high light collimating efficiency.
In order to achieve the above object, a preferred embodiment of the present invention provides a backlight device for a liquid crystal display device, including: a light source providing light; a light waveguide plate guiding light from the light source, having an emitting surface, a front surface and a bottom surface, the emitting surface being adjacent to the light source; a reflector arranged under the bottom surface of the light wave guide plate, reflecting light; and at least one cholesteric liquid crystal (CLC) film arranged over the front surface of the light wave guide plate, collimating light.
The CLC film has a one-layered structure of one of either a right- or a left handed CLC layer, wherein the right- and left handed CLC layer selectively reflect right- and left-handed circularly polarized light, respectively. The CLC film may also have a dual-layered structure of a right- and a left handed CLC layer, wherein the right- and left handed CLC layer selectively reflect right- and left-handed circularly polarized light, respectively. The backlight device further includes a prism sheet arranged between the CLC film and the front surface of the light wave guide plate.
By using the backlight device according to preferred embodiments of the present invention, light collimating efficiency and brightness can be improved.